In recent years there has been growing interest in the use of artificial materials, particularly materials formed from polymers, for use in implantable devices that come into contact with bodily tissues or fluids particularly blood. Some examples of such devices are artificial heart valves, stents and vascular prosthesis. Progress in this area has, however, been hampered somewhat by the thrombogenicity of many polymer materials. Reference is made to M. Szycher, J. Biomat Appln (1998) 12: 321 in that regard.
Efforts to overcome the problems associated with thrombogenicity of polymer materials used in the production of implantable devices have not met with a great deal of success to date. Some examples of approaches that have bee attempted include heparinization (S. W. Kim, C. D. Ebert, J. Y. Lin, J. C. McRea Am Soc Artif Internal Organs (1983) 6: 76), physical modification of the surface (K. Webb, W. Hlady, P. A Tresco, J. Biomed Mat Res (1998) 41: 421-430; E. W. Merrill, Ann NY Acad Sci (1977) 6: 283-290) and increasing surface hydrophilicity (S. J. Sofia, E. W. Merrill, in “Polyethylene Glycol; Chemistry and Biological Applications”, J. M. Harris and S. Zalipsky (eds.), American Chemical Society (1997) Ch. 22). Although these methods have met with some commercial viability, they are mainly useful for short-term applications, such as in catheter or in dialysis tubing. This is because many of the chemical and physical modifications of the device surfaces have limited shelf-life, both ex vivo and in vivo. Moreover, the methods involved in the production of implantable devices using these approaches are both elaborate and intricate.
Attempts have also been made to minimize thrombus formation by promoting endothelialization of the surface of an implantable device that contacts bodily fluids or tissues in use as described, for example, in U.S. Pat. No. 5,744,515, which relates to modification of a porous material with adhesion molecules, and U.S. Pat. No. 6,379,383, which relates to deposition of the material used to form the device so as to control surface heterogenities.